Figure 3. Cytoplasmic ribosomes primed... | Rockefeller University Press

Figure 3.

$Cytoplasmic ribosomes primed for protein import cluster on the mitochondrial membrane. (A) Quantification of the maximum value of K(r)/KCSR(r) for a 30–40-nm radius for each tomogram within the indicated ribosome class. Quantification from import-oriented ribosomes n = 87 and non-import-oriented ribosomes n = 89 tomograms are shown. P values from Mann–Whitney U test are indicated. ****P < 0.001. (B) Representative membrane surface reconstructions of mitochondria (gray) with ribosomes oriented for import relative to the OMM (blue). Insets show zoomed-in boxed regions of the ribosome models with circle overlays demarking the location of the 3′ mRNA entry (blue), the 5′ mRNA exit sites (orange), the possible pathways of interconnecting mRNA (dashed black line), and the calculated end-to-end distance from 5′ to 3′ of each interconnected mRNA (solid black line). (C) Representative tomogram slices showing labeled cytoplasm, ribosome, mitochondrial matrix, IMM, OMM, and CJs (upper panel) with an overlay of the surface mesh reconstructions of the IMM and OMM (red) and ribosome (blue) (lower panel). (D) Representative membrane surface reconstruction of mitochondria with the OMM surface colored by OMM–IMM membrane distance and the IMM surface shown in gray. The bottom inset labeled “1” shows inner membrane boundary (IBM) regions on OMM with more subtle OMM–IMM distance variations. In contrast, the bottom inset labeled “2” shows regions on OMM with large OMM–IMM distances corresponding to CJs. (E) Ribosome and membrane models defining the patches on the membrane surface mesh reconstruction that correspond to ribosomes oriented for import (blue, top) and ribosomes near but not oriented for import (pink, bottom). The ribosomes oriented for import are defined as those with the peptide exit tunnel (yellow arrow) pointed toward the membrane. In contrast, those not oriented for import have peptide exit tunnels facing away from the membrane. (F) Representative ribosome and membrane model with the OMM surface colored by the ribosome-associated (blue) and crista-associated OMM (orange), with areas of overlap (black). (G) Quantification of the average fraction of overlap from each tomogram between indicated ribosome class. Quantification from import-oriented ribosomes n = 71, non-import-oriented ribosomes n = 71, and random n = 71 tomograms are shown. P values from Mann–Whitney U test are indicated. *P < 0.05; ****P < 0.001.$

Cytoplasmic ribosomes primed for protein import cluster on the mitochondrial membrane. (A) Quantification of the maximum value of K(r)/K_CSR(r) for a 30–40-nm radius for each tomogram within the indicated ribosome class. Quantification from import-oriented ribosomes n = 87 and non-import-oriented ribosomes n = 89 tomograms are shown. P values from Mann–Whitney U test are indicated. ****P < 0.001. (B) Representative membrane surface reconstructions of mitochondria (gray) with ribosomes oriented for import relative to the OMM (blue). Insets show zoomed-in boxed regions of the ribosome models with circle overlays demarking the location of the 3′ mRNA entry (blue), the 5′ mRNA exit sites (orange), the possible pathways of interconnecting mRNA (dashed black line), and the calculated end-to-end distance from 5′ to 3′ of each interconnected mRNA (solid black line). (C) Representative tomogram slices showing labeled cytoplasm, ribosome, mitochondrial matrix, IMM, OMM, and CJs (upper panel) with an overlay of the surface mesh reconstructions of the IMM and OMM (red) and ribosome (blue) (lower panel). (D) Representative membrane surface reconstruction of mitochondria with the OMM surface colored by OMM–IMM membrane distance and the IMM surface shown in gray. The bottom inset labeled “1” shows inner membrane boundary (IBM) regions on OMM with more subtle OMM–IMM distance variations. In contrast, the bottom inset labeled “2” shows regions on OMM with large OMM–IMM distances corresponding to CJs. (E) Ribosome and membrane models defining the patches on the membrane surface mesh reconstruction that correspond to ribosomes oriented for import (blue, top) and ribosomes near but not oriented for import (pink, bottom). The ribosomes oriented for import are defined as those with the peptide exit tunnel (yellow arrow) pointed toward the membrane. In contrast, those not oriented for import have peptide exit tunnels facing away from the membrane. (F) Representative ribosome and membrane model with the OMM surface colored by the ribosome-associated (blue) and crista-associated OMM (orange), with areas of overlap (black). (G) Quantification of the average fraction of overlap from each tomogram between indicated ribosome class. Quantification from import-oriented ribosomes n = 71, non-import-oriented ribosomes n = 71, and random n = 71 tomograms are shown. P values from Mann–Whitney U test are indicated. *P < 0.05; ****P < 0.001.

This Feature Is Available To Subscribers Only